Fixed wing surface effect craft

ABSTRACT

A fixed wing surface effect craft utilizing two streamlined hulls for travel on water. The spaced apart hulls carry an airfoil between them for producing aerodynamic lifting forces. As the craft moves forward through the water, a Venturi chamber is produced beneath the wing to provide an air cushion which raises the craft onto the water surface to reduce the frictional drag and allow the craft to move across the surface of the water at high speeds with minimal power requirements. An inverted-V tail is carried aft and above the craft and lateral control surfaces are located on the sides of the hulls to provide means for control and stabilization of the craft.

United States Patent 1 Austin 1 1 FIXED WING SURFACE EFFECT CRAFT [75] Inventor: Thomas M. Austin, Fargo. N. Dak.

[73] Assignee: Austin Aeromarine. Inc.. Fargo. N.

Oak.

[22] Filed: June 24, 1974 [21] Appl. No.: 482,342

1 1 Nov. 11, 1975 3.8041149 4/1974 Greer 114/67 A FORE1GN PATENTS OR APPL1CAT1ONS 1.053.294 2/1954 France 244/87 Primary Exuminer-Trygve M. Blix Ass/smut liruminer-Gregory W. OConnor [57] ABSTRACT A fixed wing surface effect craft utilizing two stream- 1ined hu11s for travel on water. The spaced apart hulls curry an airfoil between them for producing aerodynamic lifting forces. As the craft moves forward through the water. a Venturi chamber is produced he neath the wing to provide an air cushion which raises the craft onto the water surface to reduce the frictional drag and allow the craft to move across the surface of the water at high speeds with minimal power requirements. An inverted-V tail is carried aft and above the craft and lateral control surfaces are located on the sides of the bulls to provide means for control and stabilization of the craft.

14 Claims, 4 Drawing Figures U.S. Patent Nov. 11, 1975 3,918,382

FIXED WING SURFACE EFFECT CRAFT BACKGROUND OF THE INVENTION 1. Field of the Invention Fixed Wing Surface Effect Craft utilizing an inverted- V tail and outboard control surfaces.

2. Description of the Prior Art Surface effect vehicles or craft, which are also known as ground effect machines, can be generally described as vehicles which are propelled forward by various means and which utilize a cushion of air beneath them to reduce the friction encountered between the base of the vehicle and the surface over which it is traveling. Surface effect vehicles are generally intended for travel over the surface of a body of water or over a combination of terrain including a water surface and ground surface. Because the frictional force between the vehicle and the surface over which it is traveling is reduced by the cushion of air beneath the vehicle, the power requirements for the vehicle are greatly reduced.

Broadly speaking, there are two general types of surface effect vehicles. One is the non-wing or fan type and the other is the fixed wing design. In addition, some designs incorporate both a fan and a fixed wing. The fan type vehicle utilizes a powered fan or propellor for drawing air into the vehicle and creating a high pressure area beneath the vehicle which produces the air cushion on which the vehicle rides. The fixed wing design utilizes an airfoil to dynamically create a lifting force and a friction-reducing cushion beneath the vehicle by the forward velocity of the airfoil. Because of the aerodynamic forces acting on the airfoil, a lift force is exerted on the vehicle which tends to raise it above the surface on which it is riding. In addition, high pressure air is entrapped beneath the airfoil to create an air cushion which also tends to raise the vehicle above the surface on which it is traveling.

Referring to the fixed wing design for surface effect vehicles, if the vehicle is being operated on water, the airfoil can be utilized to either lift the vehicle entirely above the water surface or to merely raise it such that only part of the vehicle is contacting the water surface, usually the aft portion. At low operating speeds, these vehicles are operated much like standard, substantially immersed boats. As the speed is increased, the aerodynamic forces raise the vehicle at least partially above the water surface. Thus, such vehicles must be designed so that they operate in two regimes, a hydrodynamic regime wherein the boat is brought up to speed while substantially immersed in the water, and an aerodynamic regime where aerodynamic forces are utilized to elevate and partially control the vehicle while it is propelled at high speeds.

When a fixed wing surface effect vehicle design is utilized which is operable both as a standard boat and as a craft which is partially elevated out of the water on an air cushion, significant problems are encountered in providing stability and control for the craft. A combination of aerodynamic and hydrodynamic forces must be taken into account in designing the vehicle and the control surfaces and hull of the vehicle must be designed to operate both in a primarily hydrodynamic regime and primarily in an aerodynamic regime. Such dual-mode operating requirements pose problems which have made it difficult in the past to design a fixed wing surface effect craft which is both stable and easily controlled while operating both as a conventional boat and as an air-cushion elevated surface effect craft.

SUMMARY The present invention is a fixed wing surface effect craft which is carried through water on twin hulls as a conventional boat and which can be raised partially out of the water by creation of an air cushion beneath the craft. The air cushion is formed as the craft moves forward by aerodynamic forces operating on an airfoil carried between the twin hulls The airfoil provides lift for the craft and also provides a Venturi chamber beneath the craft which creates the air cushion for supporting the craft and reducing the friction between it and the water surface. An inverted-V tail is attached to the craft in combination with lateral control surfaces for controlling the attitude and stability of the craft. The design of the tail, the lateral control surfaces and the positioning of the airfoil relative to the twin hulls provides a surface effect craft which can attain high speeds, is stable and can be controlled in both lateral and longitudinal directions. In addition, the design of the craft allows a fan to be utilized as a second means creating the necessary air cushion for raising the craft out of the water. Various jet, water propellor or other propulsion systems can be utilized for propelling the craft.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of the surface effect craft;

FIG. 2 is a top plan view of the surface effect craft;

FIG. 3 is a front elevational view of the surface effect craft; and

FIG. 4 is a sectional view of the surface effect craft along the line 4-4 in FIG. 2 showing the airfoil section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1-4, wherein like numerals refer to like structural elements, the fixed wing surface effect craft 1 is comprised of two streamlined hulls, each denoted by thenumeral 10, a central airfoil 20 and an inverted-V tail 31. Two lateral control surfaces, each designated by the numeral 40, are located on the outer sides of hulls 10 for providing longitudinal control and stability.

The surface effect craft 1 can be powered by various means which will be described in detail later. As the craft moves across a water surface, hulls 10 support the craft on the water. As the speed of surface effect craft 1 increases, the speed of the air passing over the airfoil 20 increases, producing aerodynamic lift. In addition, air is driven beneath airfoil 20 into a Venturi-chamber formed beneath airfoil 20 for producing an air cushion which will be described in detail later. The lifting effect of the aerodynamic forces and the air cushion tend to raise the craft substantially out of the water. At its maximum velocity, only the back portion of hulls 10 remain immersed in the water. As a result of this elevation of the craft, the frictional drag between the craft and the water is greatly reduced, allowing it to travel up to I35 miles per hour or more on the water surface. Alternate means (not shown) for producing the air cushion beneath the surface effect craft 1 may also be utilized and they will be described in detail later.

The surface effect craft 1 is generally symmetrical about a longitudinal vertical plane located along the centerline of the craft. This plane is designated by the numeral 2 in FIG. 2. In the description of the preferred embodiment. when reference is made to symmetrically disposed elements on either side of the craft, it will be presumed that these elements are symmetrically disposed about the vertical plane of symmetry 2 unless note is made to the contrary.

Referring specifically to symmetrically disposed hulls 10, each is comprised of a streamlined front portion 1 I, a top surface 14, a bottom surface 13 and a back end 12. A generally planar inner side 15 is positioned nearest the plane of symmetry 2 and streamlined outer side 16 forms the exterior surface of hulls 10. In the preferred embodiment, the hull back end 12 is generally planar and vertical with respect to the hull bottom surface 13. This type of hull back end is particularly adaptable to the placement of an outboard motor 50 or an inboard-outboard motor for use as a power means. Other types of power means may also be utilized and in certain instances it may be desirable to have a different contour for the hull back end 12.

A line AA connecting the opposed outside lower edges of the hull back ends 12 is referred to as the hull baseline". The distance between these outboard points along line AA is referred to as the craft beam. The hull baseline AA and the beam length will be referred to later in describing the positioning of various elements of the craft.

The streamlined hull front portion 1 1 shown in FIGS. I and 2 has been found particularly beneficial in providing stability to the craft 1 and in reducing the profile drag of the craft 1. Other variations of the streamline shape may also be utilized where appropriate. The hull bottom surface 13 is shown in FIG. 3 as being generally planar and sloping outwardly and upwardly from inner hull side 15. As the surface effect craft 1 moves foward and gains speed, the air cushion produced beneath the airfoil raises the craft onto the water surface where only the back portion of the hull bottom surface 13 is riding in the water. If the power source for the craft utilizes a submerged propellor 51 it would be located generally adjacent the submerged aft portion of bottom surface 13 so that it would remain submerged during operation of the craft. It has been found that generally planar vertical inner sides 15 of surface effect craft 1 provide good aerodynamic flow characteristics over the airfoil 20 which is positioned between the inner sides 15 of hulls 10. Two vertical closure members, each designated by the numeral 17, extend back from the inner side 15 of each of hulls 10. The vertical closure members 17 extend to the trailing edge of the airfoil 20. This is shown in FIGS. 1, 2 and 4. The pur pose of vertical closure member 17 is to complete the enclosure of the sides of the airfoil 20 from its leading edge 24 to its trailing edge 25.

The hull top surface 14 is generally planar over approximately the aft two-thirds of the hulls l0 and slopes downwardly over the front portion 11 to form a streamlined front end for the hulls l0. Cockpits 18 (FIG. 2) are located within each of hulls 10 to provide a position for the pilot of the craft. Other suitable locations for the craft pilot may also be provided. The hulls 10 may be hollow to provide for storage capacity or for fuel. In addition, control systems and the like may also be carried in the hulls l0.

tail in FIG. 4, airfoil 20 has a leading edge 24, a trailing edge 25, a bottom surface 22 and a top surface 23. As will be appreciated by a person skilled in the art, a chordline 21 extending from the leading edge 24 to the trailing edge 25 partially describes the dimensional character of the airfoil cross section. The halfchord position" to be referred to later is the midpoint of chordline 21. In the preferred embodiment shown in FIGS. 1-4, the cross section of the airfoil 20 is constant across the width of the airfoil between the inner sides 15 of bulls 10. In other embodiments (not shown) the cross section of airfoil 20 may vary across the width of the airfoil. In addition, the airfoil 20 shown in FIG. 4 has a planar bottom surface 22. Here. also, a different bottom surface (not shown) may be utilized where appropriate. In addition, various airfoil cross sections (not shown) may be utilized for airfoil 20 in different ranges of operating speed and in different weight ranges for the craft 1.

Airfoil 20 has two general purposes. It is intended to produce an aerodynamic lift which tends to raise the surface effect craft 1 partially out of the water. Secondly, it is intended to help create a Venturi-chamber beneath airfoil 20 which in turn produces an air cushion for partially supporting the surface effect craft 1 on top of the water surface. Such an air cushion greatly reduces the frictional drag force acting between the base of the craft 1 and the water surface. This allows the craft 1 to be propelled at very high speeds (up to I35 miles or greater) without a great increase in the power requirement.

To produce the Venturfchamber beneath the airfoil 20, the bottom surface 22 of airfoil 20 is positioned above the bottom surfaces 13 of hulls 10. This produces a four-sided chamber bounded by a portion of the hull inner sides 15, the airfoil bottom surface 22 and the water surface. The cross-sectional profile of the Venturi chamber along plane 2 is varied as craft 1 raises up on the water. When the craft 1 is at rest in the water, the Venturi-chamber profile is slightly tapered in an aft direction. This results from the fact that airfoil 20 has a positive angle of incidence relative to the hull bottom surface 13. In the preferred embodiment shown in the figures, this positive angle of incidence is 1V2".

As is shown in FIG. 4, a control flap 26 is built into the trailing edge 25 of airfoil 20. The control flap 26 has two general purposes. First, when it is deflected downward or upward the aerodynamic characteristics of airfoil 20 are varied. This in turn varies the lift, drag and moments imparted to craft 1 by the airfoil. Secondly, when control flap 26 is deflected downward, it further encloses the back end of the Venturi-chamber created beneath airfoil 20. As is well known in aerodynamics, when a Venturi-chamber is formed having a restricted or narrowed cross sectional area in it, various changes in static pressure and in the velocity of the air passing through it are produced. In the surface effect craft design shown in FIGS. 15, it has been found through experimentation and trial runs of numerous iterative designs of the craft that the Venturi-chamber produced by airfoil 20 and hulls l creates an air cushion beneath surface effect craft 1. This air cushion exerts a force on the bottom surface 22 of airfoil 20 which raises the front portion of craft 1 above the surface of the water while allowing the back portion of hull bottom surfaces 13 to remain submerged. The height to which the surface effect craft 1 is raised above the water surface may be varied by moving control flap 26 to various downwardly deflected positions. In addition, the height is varied by movement of other control means which will be described in detail later. Thus, as the surface effect craft 1 is propelled forward, the aerodynamic forces acting on airfoil 20 produce aerodynamic lift and also produce forces on the bottom surface 22 as a result of the Venturi chamber which is formed beneath the craft. The effect of these forces is to create an air cushion on which. the surface effect craft 1 can ride which in turn results in a decrease in frictional drag between the craft 1 and the water.

As was described above, the air cushion beneath airfoil 20 is produced only when the surface effect craft 1 moves forward and the moving air creates aerodynamic forces on and beneath airfoil 20. Thus, an air cushion is not produced until the craft 1 is moving forward at sufficient speed to create aerodynamic forces. As a supplemental means for producing the desired air cushion (shown by dotted lines in H6. 3), a fan or propellor 61 may be utilized in combination with this fixed wing design to create an air cushion beneath airfoil 20. These auxiliary lifting means dotted by the numeral 60, may be utilized to initially raise the surface effect craft 1 above the water before it has developed sufficient forward speed to dynamically produce the air cushion beneath bottom surface 22. Such an alternative embodiment would generally consist of a fan or a propellor 61 located within the surface effect craft 1 which directs air downward through airfoil 20 to the area beneath bottom surface 22. This pressurized air beneath bottom surface 22 would tend to raise surface effect craft 1 above the water surface. To produce the necessary air cushion for this alternative embodiment would.

require that control flap 26 be deflected to a generally vertical downward position and also that a skirt flap 28, which is located on the airfoil bottom surface 22, be lowered. Skirt flap 28 and control flap 26 would then enclose the area beneath airfoil 20 to allow the pressurized air from the fan (not shown) to be captured so that an air cushion would be produced. Once the surface effect craft 1 raises out of the water, the friction between the craft and the water surface would be reduced and it could be propelled forward at sufficient velocity to dynamically create an air cushion beneath the airfoil 20. When this speed has been attained, the skirt flap 28 would be raised to a position where it was flush with bottom surface 22 and control flap 26 would be raised up to allow the moving air to create an air cushion in the Venturi-chamber beneath the airfoil bottom surface 22.

According to well known aerodynamic principles, a craft which is partially dependent on aerodynamic forces to elevate it, can also be controlled by other an odynamic forces. It is the intent of the controlling aerodynamic forces to stabilize the craft as it moves through the water and to also produce control forces and moments which tend to steer the craft. In the embodiment shown in the Figures, stability and steering control are provided in several ways. First, referring to FIG. 4, a spoiler 27 is located in the top surface 23 of airfoil 20. As is well known in aerodynamics, when spoiler 27 is raised, the lifting characteristics of airfoil 20 are varied. Such variation of lift characteristics changes the pitching moment of the airfoil 20 which in turn affects the longitudinal stability of the surface effect craft 1. This stability tends to control the elevation of the craft out of the water. In addition, alternative means for changing the aerodynamic characteristics of airfoil 20 may also be incorporated. These are now shown specifically in the Figures, but could involve such features as slots cut in the airfoil 20 at various locations both on the forward and the aft portions of the airfoil. In addition, various boundary layer control devices which are well known in the aerodynamic art could be incorporated into airfoil 20.

To further control the stability and movement of surface effect craft 1, the present invention describes the preferred location of the craft center of gravity and the one-half chord position of airfoil 20 with respect to the center of gravity to provide a stable craft which can be effectively controlled. It has been found through much experimentation and iterative design, that the center of gravity of the surface effect craft 1 should be located forward of the hull baseline AA a distance between 55 and 100 percent of the beam length. In addition, it has been found that the best position for the one-half chord point of airfoil 20 is forward from the hull baseline AA a distance between 50 and percent of the beam length. This positioning of the craft center of gravity and the one-half chord position of airfoil 20 has been found to produce a stable and easily controlled surface effect craft design.

The lateral control surfaces 40 located on the outer sides 16 of hulls 10 are utilized to produce lateral and longitudinal control for the surface effect craft 1. In the embodiment shown in the Figures, the lateral control surfaces 40 are airfoils having a leading edge 40a and are all-moving. In the preferred embodiment, they pivot about the one-third chord point aft of the leading edge 40a. By pivoting the lateral control surfaces 40 either symmetrically or asymmetrically, the lift which they produce varies and as a consequence, a pitching or roll moment, respectively, can be imparted to the surface effect craft 1. When a roll moment is imparted, the craft yaws to vary the forward direction. This allows the surface effect craft 1 to be steered right or left in its forward direction by controlling the pitch of lateral control surfaces 40. It has been found that when the one-half chord point of lateral control surfaces 40 is positioned forward of the hull baseline AA a distance equal to 50-90 percent of the craft beam length, the best functioning of surfaces 40 and craft 1 is achieved.

To produce longitudinal stability and to provide control means for varing both the longitudinal and lateral attitude of surface effect craft 1, the inverted-V tail 31 has been provided. As is shown in FIGS. 1-3, tail 3] is comprised of two opposed tail panels. each designated by the numeral 32, which join at an apex 32a and slant downwardly and outwardly to an outboard edge 32b. The tail 31 is attached to the hulls 10 by means of two tail booms, each designated by the numeral 33. Each of the tail booms 33 extends aft and upward from the hulls l0 and attach to each of the tail panels 32. In the pre ferred embodiment shown in the Figures, the leading edge 32c of tail panel 32 is located aft of the craft center of gravity :1 distance of 150% beam. The outboard edge 32b is positioned above the hull baseline AA a distance of l7r of beam.

By using the inverted-V tail arrangement shown in FIGS. 1, 2 and 3, the present invention provides a stable surface effect craft 1 which can be effectively controlled in both pitch. yaw and roll. This is partially achieved by use of the inverted tail panels 32. Because these tail panels are positioned so that they have both a horizontal and a vertical profile, they provide control surfaces in both pitch and yaw. lf tail panels 32 are pivoted or if aelerons or flaps 32e are added to the trailing edges 32d of tail panels 32, deflection of such control surfaces or of the entire tail panel 32 can provide the necessary aerodynamic moments for varing the lateral or longitudinal orientation or stability of the surface effect craft 1. Such movable panels may be rotated sym metrically or asymmetrically to provide a roll moment. It has been found through experimentation and iterative design that tail panels 32 are most advantageously utilized if they are each attached to a tail boom 33 at a point between the outboard edge 32b and a point midway between apex 32a and edge 32b and generally near leading edges 32c.

Because of the advantageous aerodynamic and hydrodynamic characteristics achieved by the present design, it can be utilized in any application where it is desired to provide a device which rides partially out of the water due to forward speed. The present embodiment has been designated as a device useful as a surface craft for carrying personnel, cargo and the like. in addition, the aerodynamic design revealed in the present invention could be used for an aircraft float or for other applications where it is desired that a device be carried across a water surface on a friction-reducing air cushion.

Various sizes of the present design may be utilized for different purposes. The present embodiment has been constructed as a prototype craft having a gross weight, including two pilots and fuel, of approximately one ton. The beam is 7 feet and the overall length is feet, 9 inches. it is intended that this prototype be operated using two outboard motors mounted at the hull back ends 12. Each motor would be capable of developing 4 135 horsepower to propel the craft at speeds in excess of 145 miles per hour.

The operation of surface effect craft 1 can be briefly described as follows. When it is desired that the craft be run at low speeds as a conventional boat which cuts through the water. power is supplied to surface effect craft 1 by a submerged propellor, a jet or other power means (not shown) to propel the craft slowly through the water. When it is desired that high speeds be at tainedl maximum power is applied to surface effect craft 1. As the craft gains speed, air begins to move over airfoil 20 producing various aerodynamic effects. A lift force is produced and an air cushion begins to build up beneath airfoil 20 in the Vcnturi-chamber beneath bottom surface 22. The buildup of an air cushion can be enhanced by movement of control flap 26 to a proper position. When the surface effect craft 1 has reached a sufficient speed. the dynamically produced air cushion in the Venturi-chamber is sufficient to raise the front portion of surface effect craft 1 out of the water. In this position. only the rear portion of hull bottom surface 13 remains in the water, e.g. the aft 6 percent length of bottom surface 13. With the surface effect craft 1 riding on the air cushion, the friction between the craft and the water is greatly reduced. As a result. the surface effect craft 1 gains considerable speed without a proportional increase of power. Speeds up to miles per hour and greater may be attained. As higher speeds are attained, the aerodynamic forces acting on airfoil 20 and the various control surfaces will vary. To maintain the stability of surface effect craft 1 as these aerodynamic forces vary, the various control means, including control flap 2S, spoiler 27, lateral control surfaces 40 and tail 31 can be utilized to control the stability and the direction of movement of surface effect craft 1.

To vary the forward direction of surface effect craft 1, lateral control surfaces 40 can be used to impart a roll moment to the craft or movable tail panels 32 or tail flaps (not shown) may be moved to produce aerodynamic moments for varing the yaw direction of the craft. Also, if immersed props are used for power. their direction or speed can be varied. To control the pitching moment of the craft and its position relative to the water surface, control flaps 26, spoiler 27 or tail 31 may be used in a similar manner by varing the position of the various elements. Various aerodynamic breaking devices (not shown) may also be added to the craft as required.

The design of surface effect craft 1 is intended to take advantage of aerodynamic ground effects which result when a vehicle moves adjacent to the ground or water surface. it has been found that the preferred embodiment of surface effect craft 1 operates effectively in a range of heights above the water surface where the trailing edge 25 of airfoil 20 is positioned above the water surface a distance between 5 and 20 percent of the length of airfoil chordline 21. This height is varied as the control flap 26 is deflected.

What is claimed is:

1. A fixed wing surface effect craft for travel on wa ter, said craft being generally symmetrical about a longitudinal vertical plane along its centerline and being described in part by a craft center of gravity, comprismg:

a. two symmetrically disposed streamlined hulls for supporting the craft on water, said hulls including a tapered front portion, a back end. a bottom surface, an outer side and a inner side; said hull bottom surface having a supporting back portion which generally contacts the water when the craft is propelled therethrough and which serves as a point of support for the craft; a line extending between two opposed points, each located on said hull back ends where the hull outer side and bottom surface meet. defining a hull baseline positioned adjacent said bottom surface supporting portion, and having a length referred to as the craft beam;

b. an airfoil laterally disposed between said hulls to provide aerodynamic lift for raising the craft onto the water surface;

c. said airfoil having a leading edge, a trailing edge and a bottom surface; said airfoil fixedly oriented between the inner sides of said hulls to provide a positive angle of incidence between the airfoil and the Water surface when the craft is moving forward;

d. said airfoil oriented on the craft with its bottom surface located above the bottom surface of said hulls to form a Venturi-shaped chamber beneath the craft for creating an air cushion that partially supports the craft and allows a major portion of the bottom surface of said hulls to rise out of the water as the craft moves foward, said chamber bounded by the inner sides of said hulls, the airfoil bottom surface and the water surface;

e. symmetrically disposed control and stabilization means including an inverted-V tail assembly positioned above and aft of the supporting back portion of said hull bottom surface; said tail assembly being comprised of non-vertical control surfaces, including two inclined surfaces joined at an apex edge with each surface sloping downwardly and outwardly therefrom to an outboard edge, and means for attaching said tail assembly to said hulls;

f. said control and stabilization means further including a control flap formed from at least a portion of the trailing edge of said airfoil, said flap pivotally mounted for controlled selective positioning to vary the aerodynamic characteristics of said airfoil and to vary the airflow characteristics in said Venturi chamber to partially control the lifting force imparted to the craft therefrom; and

g. stowage means for placement of personnel and cargo on the craft.

2. The craft of claim 1 including power means for propelling the craft on a water surface.

3. The craft of claim 2 wherein said power means include a water propellor and a power source, said propellor mounted to the craft for immersed operation and operatively connected to said power source.

4. The craft of claim 1 wherein the center of gravity of the craft is located forward of said hull baseline a distance between 55 and 100 percent of the craft beam.

5. The craft of claim 4 wherein said airfoil is a contant-section airfoil defined in part by a chordline, said airfoil positioned between said hulls with the center of the chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam.

6. The craft of claim 1 wherein said control and stabilization means further include a lateral control surface attached to the outer side of each of said hulls, said surface generally perpendicular to the vertical plane of symmetry of the craft and pivotable about an axis perpendicular to the vertical plane of symmetry, for producing a roll moment to the craft when properly posi tioned.

7. The craft of claim 6 wherein said lateral control surfaces are constant-section airfoils defined in part by a chordline, said lateral control surfaces positioned on said hulls with the center of said chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam.

8. The craft of claim 1 wherein said inverted-V tail is located above and aft of said hulls, each of said tail surfaces is attached to said hulls by a tail boom affixed to each of said hulls, and each of said booms is attached to a tail surface at a point between the tail surface outboard edge and the lateral centerline of said tail surface.

9. The craft of claim 8 wherein each of said tail surfaces contains a movable flap portion which can be selectively positioned for lateral and longitudinal control of the craft.

10. The craft of claim 1 wherein said control and stabilization means further include an aerodynamic spoiler movably mounted on the top surface of said airfoil, said spoiler selectively positionable to vary the aerodynamic characteristics of said airfoil.

11. The craft of claim 1, including:

a. a skirt flap pivotally mounted to said airfoil bottom surface and extending between said hulls, said flap movable to a generally vertical position to enclose the area beneath said airfoil when said control flap is pivoted downwardly; and

b. fan means for creating a volume of high pressure in the enclosed area beneath said airfoil, said high pressure creating an air cushion to raise the craft onto the water surface thereby reducing surface friction as the craft moves forward.

12. The craft of claim 1 wherein the sides of said airfoil upper surface are bounded by planar surfaces from the leading to the trailing edge to reduce airfoil edge effects.

13. A fixed wing surface effect craft for travel on water, such craft being generally symmetrical about a longitudinal vertical plane along its centerline and comprising:

a. two symmetrically disposed streamlined hulls for supporting the craft on water, each said hulls in cluding a tapered front portion, a back end, a bottom surface, an outer side and a generally planar inner side; a line extending between two opposed points, each located on said hull back ends where the hull outer side and bottom surface meet, defining a hull baseline having a length referred to as the craft beam;

b. a single central airfoil laterally disposed between side hulls to provide aerodynamic lift for raising the craft onto the water surface;

c. said airfoil having a leading edge, a trailing edge and a bottom surface; said airfoil fixedly oriented between the inner sides of said hulls to provide a positive angle of incidence between the airfoil and said hull bottom surface;

d. said airfoil oriented on the craft with its bottom surface located above the bottom surface of said hulls to form a Venturi-shaped chamber beneath the craft for creating an air cushion that partially supports the craft and allows the major portion of the bottom surface of said hull to rise out of the water as the craft moves forward, said chamber bounded by the inner sides of said hulls, the airfoil bottom surface and the water surface;

e. symmetrically disposed control and stabilization means including:

i. an inverted-V tail assembly located above and aft of said hulls, said tail having two inclined surfaces joined at an apex edge with each surface sloping downward therefrom to an outboard edge; said tail surfaces attached to said hulls by a tail boom affixed to each of said iiulls, each of said booms being attached to a tail surface at a point between the tail surface outboard edge and the lateral centerline of said tail surface;

ii. a control flap formed from the trailing edge of said airfoil, said flap pivotally mounted for controlled positioning to vary the aerodynamic characteristics of said airfoil and said Venturichamber to partially control the lifting force imparted to the craft therefrom; and

iii. lateral control surfaces attached to the outer side of each of said hulls, said surfaces generally perpendicular to the vertical plane of symmetry of the craft and pivotable about an axis perpendicular to the vertical plane of symmetry for producing a roll moment to the craft when properly positioned, said surfaces having an airfoil cross section and being pivoted at the one-third chord point from the surface leading edge;

f. the center of gravity of the craft being located forward of said hull baseline a distance between 55 and I percent of the craft beam;

g. said central airfoil being a constant-section airfoil defined in part by a chordline, said central airfoil positioned between said hulls with the center of the chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam;

h. said lateral control surfaces being constant-section 14. The craft of claim 13 including power means which include a water propellor and a power source, said propellor mounted to the craft generally adjacent said hull back end, said propellor operatively connected to said power source. 

1. A fixed wing surface effect craft for travel on water, said craft being generally symmetrical about a longitudinal vertical plane along its centerline and being described in part by a craft center of gravity, comprising: a. two symmetrically disposed streamlined hulls for supporting the craft on water, said hulls including a tapered front portion, a back end, a bottom surface, an outer side and a inner side; said hull bottom surface having a supporting back portion which generally contacts the water when the craft is propelled therethrough and which serves as a point of support for the craft; a line extending between two opposed points, each located on said hull back ends where the hull outer side and bottom surface meet, defining a hull baseline positioned adjacent said bottom surface supporting portion, and having a length referred to as the craft beam; b. an airfoil laterally disposed between said hulls to provide aerodynamic lift for raising the craft onto the water surface; c. said airfoil having a leading edge, a trailing edge and a bottom surface; said airfoil fixedly oriented between the inner sides of said hulls to provide a positive angle of incidence between the airfoil and the water surface when the craft is moving forward; d. said airfoil oriented on the craft with its bottom surface located above the bottom surface of said hulls to form a Venturi-shaped chamber beneath the craft for creating an air cushion that partially supports the craft and allows a major portion of the bottom surface of said hulls to rise out of the water as the craft moves foward, said chamber bounded by the inner sides of said hulls, the airfoil bottom surface and the water surface; e. symmetrically disposed control and stabilization means including an inverted-V tail assembly positioned above and aft of the supporting back portion of said hull bottom surface; said tail assembly being comprised of non-vertical control surfaces, including two inclined surfaces joined at an apex edge with each surface sloping downwardly and outwardly therefrom to an outboard edge, and means for attaching said tail assembly to said hulls; f. said control and stabilization means further including a control flap formed from at least a portion of the trailing edge of said airfoil, said flap pivotally mounted for controlled selective positioning to vary the aerodynamic characteristics of said airfoil and to vary the airflow characteristics in said Venturi chamber to partially control the lifting force imparted to the craft therefrom; and g. stowage means for placement of personnel and cargo on the craft.
 2. The craft of claim 1 including power means for propelling the craft on a water surface.
 3. The craft of claim 2 wherein said power means include a water propellor and a power source, said propellor mounted to the craft for immersed operation and operatively connected to said power source.
 4. The craft of claim 1 wherein the center of gravity of the craft is located forward of said hull baseline a distance between 55 and 100 percent of the craft beam.
 5. The craft of claim 4 wherein said airfoil is a contant-section airfoil defined in part by a chordline, said airfoil positioned between said hulls with the center of the chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam.
 6. The craft of claim 1 wherein said control and stabilization means further include a lateral control surface attached to the outer side of each of said hulls, said surface generally perpendicular to the vertical plane of symmetry of the craft and pivotable about an axis perpendicular to the vertical plane of symmetry, for producing a roll moment to the craft when properly positioned.
 7. The craft of claim 6 wherein said lateral control surfaces are cOnstant-section airfoils defined in part by a chordline, said lateral control surfaces positioned on said hulls with the center of said chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam.
 8. The craft of claim 1 wherein said inverted-V tail is located above and aft of said hulls, each of said tail surfaces is attached to said hulls by a tail boom affixed to each of said hulls, and each of said booms is attached to a tail surface at a point between the tail surface outboard edge and the lateral centerline of said tail surface.
 9. The craft of claim 8 wherein each of said tail surfaces contains a movable flap portion which can be selectively positioned for lateral and longitudinal control of the craft.
 10. The craft of claim 1 wherein said control and stabilization means further include an aerodynamic spoiler movably mounted on the top surface of said airfoil, said spoiler selectively positionable to vary the aerodynamic characteristics of said airfoil.
 11. The craft of claim 1, including: a. a skirt flap pivotally mounted to said airfoil bottom surface and extending between said hulls, said flap movable to a generally vertical position to enclose the area beneath said airfoil when said control flap is pivoted downwardly; and b. fan means for creating a volume of high pressure in the enclosed area beneath said airfoil, said high pressure creating an air cushion to raise the craft onto the water surface thereby reducing surface friction as the craft moves forward.
 12. The craft of claim 1 wherein the sides of said airfoil upper surface are bounded by planar surfaces from the leading to the trailing edge to reduce airfoil edge effects.
 13. A fixed wing surface effect craft for travel on water, such craft being generally symmetrical about a longitudinal vertical plane along its centerline and comprising: a. two symmetrically disposed streamlined hulls for supporting the craft on water, each said hulls including a tapered front portion, a back end, a bottom surface, an outer side and a generally planar inner side; a line extending between two opposed points, each located on said hull back ends where the hull outer side and bottom surface meet, defining a hull baseline having a length referred to as the craft beam; b. a single central airfoil laterally disposed between side hulls to provide aerodynamic lift for raising the craft onto the water surface; c. said airfoil having a leading edge, a trailing edge and a bottom surface; said airfoil fixedly oriented between the inner sides of said hulls to provide a positive angle of incidence between the airfoil and said hull bottom surface; d. said airfoil oriented on the craft with its bottom surface located above the bottom surface of said hulls to form a Venturi-shaped chamber beneath the craft for creating an air cushion that partially supports the craft and allows the major portion of the bottom surface of said hull to rise out of the water as the craft moves forward, said chamber bounded by the inner sides of said hulls, the airfoil bottom surface and the water surface; e. symmetrically disposed control and stabilization means including: i. an inverted-V tail assembly located above and aft of said hulls, said tail having two inclined surfaces joined at an apex edge with each surface sloping downward therefrom to an outboard edge; said tail surfaces attached to said hulls by a tail boom affixed to each of said hulls, each of said booms being attached to a tail surface at a point between the tail surface outboard edge and the lateral centerline of said tail surface; ii. a control flap formed from the trailing edge of said airfoil, said flap pivotally mounted for controlled positioning to vary the aerodynamic characteristics of said airfoil and said Venturi-chamber to partially control the lifting force imparted to the craft therefrom; and iii. lateral control surfaces attached to the outer side of each oF said hulls, said surfaces generally perpendicular to the vertical plane of symmetry of the craft and pivotable about an axis perpendicular to the vertical plane of symmetry for producing a roll moment to the craft when properly positioned, said surfaces having an airfoil cross section and being pivoted at the one-third chord point from the surface leading edge; f. the center of gravity of the craft being located forward of said hull baseline a distance between 55 and 100 percent of the craft beam; g. said central airfoil being a constant-section airfoil defined in part by a chordline, said central airfoil positioned between said hulls with the center of the chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam; h. said lateral control surfaces being constant-section airfoils defined in part by a chordline, said lateral control surfaces positioned on said hulls with the center of said chordline located forward of said hull baseline a distance between 50 and 90 percent of the craft beam; and i. stowage means for placement of personnel and cargo on the craft.
 14. The craft of claim 13 including power means which include a water propellor and a power source, said propellor mounted to the craft generally adjacent said hull back end, said propellor operatively connected to said power source. 